1. Field of the Invention
The present invention relates to a nonaqueous electrolyte battery and to a battery pack using a nonaqueous electrolyte battery.
2. Description of the Related Art
Nonaqueous electrolyte batteries using a negative electrode containing a lithium metal, lithium alloy, lithium compound or carbonaceous material are expected as high-energy-density batteries and are being exhaustively researched and developed. Lithium ion batteries provided with a positive electrode containing LiCoO2 or LiMn2O4 as an active material and with a negative electrode containing a carbonaceous material which absorbs and releases lithium have been widely put to practical use so far. Also, with regard to the negative electrode, studies are being made as to metal oxides and alloys which are to be used in place of the above carbonaceous material. In the case of mounting a battery, particularly, in vehicles such as cars, materials superior in chemical and electrochemical stability, strength and corrosion resistance are desired as the structural material of the negative electrode to obtain a long cycle performance in a high-temperature environment and long reliability in high output. Moreover, it is demanded that batteries have high performance in cold regions in the case of mounting them in vehicles such as cars. Specifically, it is required for these batteries to have high output performance and long-cycle life performance in a low-temperature environment. On the other hand, the development of a nonvolatile and noninflammable electrolytic solution is underway to improve safety performance. However, because such an electrolytic solution brings about a deterioration in the output performance, low-temperature performance and long-cycle life performance of a battery, it has not been put to practical use yet.
Various trials have been made to improve the characteristics of a negative electrode. JP-A 2002-42889 (KOKAI) discloses that a negative electrode with a current collector made of aluminum or an aluminum alloy, which supports a specific metal, alloy or compound is used in a nonaqueous electrolyte secondary battery. Also, JP-A 2004-296256 (KOKAI) discloses that an area where a negative electrode active material layer is not formed is disposed on the negative electrode current collector described in the foregoing JP-A 2002-42889 (KOKAI) and this area is made to face a positive electrode active material layer through a separator to improve safety and reliability when a nonaqueous electrolyte secondary battery overcharges. Moreover, JP-A 2004-296256 (KOKAI) also discloses that lithium-nickel-cobalt-aluminum oxide represented by the formula, LiNi0.8Co0.15Al0.05O2 is used as a positive electrode active material. As disclosed in JP-A 2004-296256 (KOKAI), if a solid solution containing a heterogeneous element such as Al is used as a positive electrode active material, the amount of lithium absorbed in the positive electrode active material is reduced.
In the meantime, JP-A 2001-143702 (KOKAI) discloses a method using, as a negative electrode active material, secondary particles obtained by coagulating primary particles having an average particle diameter less than 1 μm which are made of a lithium titanate compound represented by the formula, LiaTi3-aO4 (0<a<3), into granules having an average particle diameter of 5 to 100 μm, to thereby suppress the coagulation of secondary particles, thereby increasing the production yield of a large-area negative electrode for large-size batteries.
Also, studies are made as to an improvement of a nonaqueous electrolyte to thereby attain low-temperature performance and high-temperature cycle life performance at the same time. However, a nonaqueous electrolyte having high ion conductivity at low temperatures tends to react easily with a positive electrode at high temperatures, leading to remarkably reduced cycle life performance.